The present invention relates, in general, to electronics and, more particularly, to methods of forming semiconductor devices and structure.
In the past, the electronics industry used switching mode power supplies to provide regulated power to electronic devices used in communications systems, aviation systems, telecommunications systems, consumer electronics, etc. A technique for providing regulated power is described in U.S. Patent Application Publication No. 2008/0246459 filed by Thomas M. Ingman and published on Oct. 9, 2008. An area of concern in these applications is power consumption in the switching mode power supplies. Techniques for lowering power consumption have been described in U.S. Patent Application Publication No. 2010/0309694 A1 filed by Wei-Hsuan Huang et al. and in Application Note AN-48, Rev. C, titled “CAPZero-Family Design Considerations,” published by Power Integrations in September 2010. Although the techniques included in these disclosures may lower the power consumption, they may not be suitable for meeting the discharge requirements of the X capacitors such as those specified in, for example, the IEC 60950 Safety guidelines for information technology equipment. In addition, they may use additional components that are large and expensive to implement and they may be lossy.
Accordingly, it would be advantageous to have a method and structure for determining whether an AC signal is coupled to a power supply. In addition, it is desirable for the method and structure to be cost and time efficient to implement.
For simplicity and clarity of illustration, elements in the figures are not necessarily to scale, and the same reference characters in different figures denote the same elements. Additionally, descriptions and details of well-known steps and elements are omitted for simplicity of the description. As used herein current carrying electrode means an element of a device that carries current through the device such as a source or a drain of an MOS transistor or an emitter or a collector of a bipolar transistor or a cathode or anode of a diode, and a control electrode means an element of the device that controls current flow through the device such as a gate of an MOS transistor or a base of a bipolar transistor. In addition, a current carrying electrode may mean a terminal or contact of a switch and a control electrode may mean an element of the switch that controls closing and opening the switch or connecting or disconnecting the terminals or contacts from each other. Although the devices are explained herein as certain N-channel or P-channel devices, or certain N-type or P-type doped regions, a person of ordinary skill in the art will appreciate that complementary devices are also possible in accordance with embodiments of the present invention. It will be appreciated by those skilled in the art that the words during, while, and when as used herein are not exact terms that mean an action takes place instantly upon an initiating action but that there may be some small but reasonable delay, such as a propagation delay, between the reaction that is initiated by the initial action and the initial action. The use of the words approximately, about, or substantially means that a value of an element has a parameter that is expected to be very close to a stated value or position. However, as is well known in the art there are always minor variances that prevent the values or positions from being exactly as stated. It is well established in the art that variances of up to about ten percent (10%) (and up to twenty percent (20%) for semiconductor doping concentrations) are regarded as reasonable variances from the ideal goal of exactly as described.
It should be noted that a logic zero voltage level (VL) is also referred to as a logic low voltage and that the voltage level of a logic zero voltage is a function of the power supply voltage and the type of logic family. For example, in a Complementary Metal Oxide Semiconductor (CMOS) logic family a logic zero voltage may be thirty percent of the power supply voltage level. In a five volt Transistor-Transistor Logic (TTL) system a logic zero voltage level may be about 0.8 volts, whereas for a five volt CMOS system, the logic zero voltage level may be about 1.5 volts. A logic one voltage level (VH) is also referred to as a logic high voltage level and, like the logic zero voltage level, the logic high voltage level also may be a function of the power supply and the type of logic family. For example, in a CMOS system a logic one voltage may be about seventy percent of the power supply voltage level. In a five volt TTL system a logic one voltage may be about 2.4 volts, whereas for a five volt CMOS system, the logic one voltage may be about 3.5 volts.